CN108470539B

CN108470539B - Pixel circuit, driving method thereof, display panel and display device

Info

Publication number: CN108470539B
Application number: CN201810608546.3A
Authority: CN
Inventors: 高雪岭; 羊振中; 王铁石; 彭锦涛
Original assignee: BOE Technology Group Co Ltd
Current assignee: BOE Technology Group Co Ltd
Priority date: 2018-06-13
Filing date: 2018-06-13
Publication date: 2020-04-21
Anticipated expiration: 2038-06-13
Also published as: US20230206832A1; WO2019237735A1; US20240112635A1; US11869423B2; CN108470539A

Abstract

A pixel circuit, a display panel, a display device and a driving method are provided. The pixel circuit comprises a data signal writing module, a driving module, a threshold compensation transistor, a first power voltage writing module and a light emitting module, wherein the driving module comprises a driving transistor. The pixel circuit, the display panel, the display device and the driving method can compensate the threshold voltage of the driving transistor, improve the uniformity of driving current, further improve the display uniformity of the display panel, and simultaneously reduce leakage current, so that the light emitting brightness of the light emitting module is consistent.

Description

Pixel circuit, driving method thereof, display panel and display device

Technical Field

The present disclosure relates to the field of display technologies, and in particular, to a pixel circuit, a driving method thereof, a display panel, and a display device.

Background

In the OLED display panel, threshold voltages of driving transistors in respective pixel units may be different from each other due to a manufacturing process, and the threshold voltages of the driving transistors may also be shifted due to an influence such as a temperature change. Therefore, the difference in threshold voltage of each driving transistor may cause uneven display on the display panel and inconsistent light emitting brightness of the light emitting device, which may affect the viewing experience of the user.

Also, currently, pixel circuits in displays (e.g., OLED displays) are typically constructed of Low Temperature Polysilicon (LTPS) Thin Film Transistors (TFTs) that have leakage current (I) when in the off state_off) Moreover, the leakage current is not smooth and has a tail-warp phenomenon, so that the voltage written into the driving transistor cannot be locked well during one frame of display picture.

Disclosure of Invention

In order to solve the above problem, a first aspect of the present invention proposes a pixel circuit, which may include: the driving module comprises a driving transistor, and the first power supply voltage writing module is connected with a first light-emitting control signal end, a first power supply voltage end, a source electrode of the driving transistor and a grid electrode of the driving transistor and is configured to write a first power supply voltage signal of the first power supply voltage end into the source electrode of the driving transistor under the control of a first light-emitting control signal of the first light-emitting control signal end; the data signal writing module is connected with the writing control end, the data signal end and the source electrode of the driving transistor and is configured to transmit the data signal of the data signal end to the source electrode of the driving transistor under the control of the writing control signal of the writing control end; a threshold compensation transistor having a gate connected to the first node, a source connected to the gate of the driving transistor, and a drain connected to the drain of the driving transistor, and configured to perform voltage compensation on the gate of the driving transistor when the first node is at an active level; and the first end of the light-emitting module is connected with the drain electrode of the driving transistor, and the second end of the light-emitting module is connected with the second power supply voltage end.

In one example, the threshold compensation transistor may be an oxide transistor.

In one example, the pixel circuit further includes: and the reference signal writing module is connected with the reference control terminal, the reference signal terminal, the first light-emitting control signal terminal and the first node, and is configured to control the potential of the first node according to the reference control signal of the reference control terminal and the first light-emitting control signal of the first light-emitting control signal terminal.

In one example, the pixel circuit further includes: and the reset module is connected with the reset control terminal, the reset potential terminal and the first terminal of the light-emitting module and is configured to reset the first terminal of the light-emitting module and the grid electrode of the driving transistor under the control of a reset control signal of the reset control terminal.

In one example, the pixel circuit further includes: and the light emitting control module is connected with the second light emitting control signal end, the drain electrode of the driving transistor and the first end of the light emitting module and is configured to drive the light emitting module to emit light under the control of a second light emitting control signal of the second light emitting control signal end.

In one example, the reference signal writing module includes: a reference signal writing transistor, the grid of which is connected with the reference control end, the source of which is connected with the first node, and the drain of which is connected with the reference signal end; and a first capacitor connected between the first light emission control signal terminal and the first node.

In one example, the data signal writing module includes: and the grid electrode of the data writing transistor is connected with the data writing control end, the source electrode of the data writing transistor is connected with the data signal end, and the drain electrode of the data writing transistor is connected with the source electrode of the driving transistor.

In one example, the first power supply voltage writing module includes: and the grid electrode of the first power supply voltage writing transistor is connected with the first light-emitting control signal end, the source electrode of the first power supply voltage writing transistor is connected with the first power supply voltage end, and the drain electrode of the first power supply voltage writing transistor is connected with the source electrode of the driving transistor.

In one example, the driving module further includes: and a second capacitor connected between the first power voltage terminal and the gate of the driving transistor.

In one example, the lighting control module includes: a grid electrode of the light-emitting control transistor is connected with the second light-emitting control signal end, a source electrode of the light-emitting control transistor is connected with a drain electrode of the driving transistor, and the drain electrode of the light-emitting control transistor is connected with the first end of the light-emitting module;

in one example, the light emitting module includes: and the anode of the OLED is used as the first end of the light-emitting module, and the cathode of the OLED is used as the second end of the light-emitting module.

In one example, the reset module includes a reset transistor having a gate connected to a reset control terminal, a source connected to the first terminal of the light emitting module, and a drain connected to a reset potential terminal.

In one example, the second power supply voltage of the second power supply voltage terminal is lower than the reset potential of the reset potential terminal.

In a second aspect of the present disclosure, there is provided a method for driving any one of the pixel circuits according to the first aspect of the present disclosure, the method may include: in a data writing and threshold value compensation stage, a writing control signal of the writing control end is at a first level, a data signal of the data signal end is written into a source electrode of a driving transistor, a reference control signal of the reference control end jumps from the first level to a second level, the level of a first light-emitting control signal jumps from the first level to the second level, the level of a first node is pulled up, and under the control of the first node, the grid potential of the driving transistor is compensated; in a light emitting stage, a second light emitting control signal of the second light emitting control signal end is at a first level, and the driving current of the driving transistor flows to the light emitting module to drive the light emitting module to emit light.

In one example, the pixel circuit further includes: the reference signal writing module is connected with the reference control end, the reference signal end, the first light-emitting control signal end and the first node; the method further comprises the following steps: the method comprises a first initialization stage and a second initialization stage, wherein in the first initialization stage, a reference control signal of a reference control end is in a first level, and the reference signal of the reference control end is transmitted to a first node; in a second initialization phase, the reference control signal of the reference control terminal jumps from a first level to a second level, the level of the first lighting control signal jumps from the first level to the second level, and the level of the first node is pulled up.

In one example, the pixel circuit further includes: the reset module is connected with the reset control end, the reset potential end and the first end of the light-emitting module; in the second initialization phase, the reset control signal of the reset control end is at the first level, and the reset potential of the reset potential end is transmitted to the first end of the light-emitting module and the grid electrode of the driving transistor.

In one example, after the pixel circuit operates for a preset time, the reference signal of the reference signal terminal is adjusted based on a shift of a threshold voltage of a threshold compensation transistor.

In one example, the pixel circuit further includes: the light emitting control module is connected with the second light emitting control signal end, the drain electrode of the driving transistor and the first end of the light emitting module; after the data writing and threshold compensation phase and before the light emitting phase, the method further comprises: and a pre-lighting stage, in which a first lighting control signal of the first lighting control signal terminal is at a first level, and a first power voltage of the first power voltage terminal is transmitted to the source of the driving transistor.

In one example, in a data writing and threshold value compensation phase, the gate potential of the driving transistor is compensated to the sum of the potential of the data signal and the threshold value potential of the driving transistor.

In one example, the first level is lower than the second level.

In a third aspect of the present disclosure, there is also provided a display panel including any one of the pixel circuits according to the first aspect of the present disclosure.

In a fourth aspect of the present disclosure, there is also provided a display device including the display panel according to the third aspect of the present disclosure.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly introduced below, and it is apparent that the drawings in the following description relate only to some embodiments of the present disclosure and are not limiting to the present disclosure.

Fig. 1 is a schematic diagram illustrating a structure of a pixel circuit according to an embodiment of the present disclosure;

fig. 2 is a specific circuit diagram showing the pixel circuit shown in fig. 1;

fig. 3 shows a flow chart of a method for driving the pixel circuit in the above-described embodiment;

fig. 4 is a timing diagram illustrating an exemplary driving of the pixel circuit shown in fig. 1 or 2;

FIGS. 5a-5e are diagrams showing the conduction states of transistors in the pixel circuit corresponding to the respective stages T1-T5 in FIG. 3; and

fig. 6 is a graph showing the relationship between the current flowing through itself and the gate-source voltage difference Vg thereof, which is simulated when different threshold voltages are set for the threshold compensation transistor M1 in the pixel circuit shown in fig. 2, and a schematic graph of the current flowing through the OLED.

Detailed Description

Various embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Here, it is to be noted that, in the drawings, the same reference numerals are given to constituent parts having substantially the same or similar structures and functions, and repeated description thereof will be omitted.

To make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. It is to be understood that the described embodiments are only a few embodiments of the present disclosure, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the disclosure without any inventive step, are within the scope of protection of the disclosure.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. The use of "first," "second," and similar terms in this disclosure is not intended to indicate any order, quantity, or importance, but rather is used to distinguish one element from another. Likewise, the word "comprising" or "comprises", and the like, means that the element or item listed before the word covers the element or item listed after the word and its equivalents, but does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

The transistors employed in all embodiments of the present disclosure may be thin film transistors or field effect transistors or other devices having the same characteristics. In this embodiment, the connection modes of the drain and the source of each transistor may be interchanged, and thus, there is no difference between the drain and the source of each transistor in the embodiments of the present disclosure. Here, only in order to distinguish two poles of the transistor except for the gate, one of the poles is referred to as a drain and the other is referred to as a source.

Fig. 1 is a schematic diagram illustrating a structure of a pixel circuit according to an embodiment of the present disclosure. As shown in fig. 1, the pixel circuit 100 includes a data signal writing module 110, a driving module 120, a threshold compensation transistor M1, a first power voltage writing module 130, and a light emitting module 140, wherein the driving module 120 includes a driving transistor DTFT.

Specifically, the data signal writing module 110 is connected to the data writing control terminal gate (n), the data signal terminal data (n), and the source of the driving transistor DTFT. The data signal writing module is used for transmitting a data signal date (n) of the data signal end to the source electrode of the driving transistor under the control of a data writing control signal of a data writing control end gate (n).

The threshold compensation transistor M1 has a gate connected to the first node N1, a source connected to the gate of the driving transistor DTFT, and a drain connected to the drain of the driving transistor DTFT. The threshold compensation transistor M1 is used to perform voltage compensation on the gate of the driving transistor DTFT when the first node N1 is at an active level.

The first power voltage writing module 130 is connected to the first light emitting control signal terminal em (n), the first power voltage terminal ELVDD, and the source electrode of the driving transistor DTFT. The first power voltage writing module is configured to write the first power voltage signal of the first power voltage terminal ELVDD to the source of the driving transistor DTFT under the control of the first light emission control signal terminal em (n).

And a light emitting module 140 having a first terminal connected to the light emitting control module and a second terminal connected to the second power voltage terminal ELVSS.

When the first node N1 is at an active level to turn on the threshold compensation transistor M1, the turn on of the threshold compensation transistor M1 makes communication between the gate and the drain of the driving transistor DTFT, thereby forming a path to adjust (e.g., reset or compensate) the voltage of the gate of the driving transistor DTFT through the drain of the driving transistor DTFT.

However, a Low Temperature Polysilicon (LTPS) Thin Film Transistor (TFT) is generally used in the conventional pixel circuit to compensate for the threshold voltage of the driving transistor DTFT, but the LTPS TFT has a current (I) when it is in an off state_off) Is obvious and I_offThe tail-warping phenomenon exists, so that the pixel circuit has leakage current and cannot well lock the voltage compensated by the Data.

In view of the aboveIn the embodiment of the present disclosure, the threshold compensation transistor M1 may preferably be an Oxide transistor Oxide TFT, which has the following advantages over LTPS TFT: current I of Oxide TFT in OFF state_offRelatively small, on the order of 1.0E-13, and I_offAnd (4) smoothing. Therefore, when Oxide TFTs are used instead of LTPSTFTs for voltage compensation, leakage current in the pixel circuit is very small, and thus the problem of non-uniformity in light emission luminance of light emitting devices in the pixel circuit can be significantly improved.

In one example, the pixel circuit 100 shown in fig. 1 may further include: the reference signal writing module 150 is connected to the first node N1 for controlling the potential of the node N1. Specifically, the reference signal writing module is further connected to a reference control terminal Gate (n-2), a reference signal terminal Vref, and a first light-emitting control signal terminal em (n). The reference signal writing module 150 is configured to control the potential of the first node N1 according to the reference control signal of the reference control terminal Gate (N-2) and the first lighting control signal of the first lighting control signal terminal em (N).

In one example, the pixel circuit 100 shown in fig. 1 may further include: and a reset module 160 connected to the reset control terminal Gate (n-1), the reset potential terminal Vint and the first terminal of the light emitting module. The reset module 160 is configured to reset the first terminal of the light emitting module under the control of a reset control signal of the reset control terminal Gate (n-1).

In one example, the pixel circuit 100 shown in fig. 1 may further include a light emission control module 170 connected to the second light emission control signal terminal EM (n +1), the drain of the driving transistor, and the light emission module, and configured to drive the light emission module to emit light under the control of the second light emission control signal terminal EM (n + 1).

Fig. 2 is a specific circuit diagram showing the pixel circuit shown in fig. 1. The pixel circuit shown in fig. 2, wherein the reference signal writing module 150 may include a reference signal writing transistor M2 and a first capacitor C1. Specifically, the reference signal writing transistor M2 has a Gate connected to the reference control terminal Gate (N-2), a source connected to the first node N1, and a drain connected to the reference signal terminal Vref. The reference signal writing transistor M2 is used to transfer the reference signal of the reference signal terminal Vref to the first node N1 under the control of the reference control signal of the reference control terminal Gate (N-2). A first capacitor C1 connected between the first emission control signal terminal em (N) and a first node N1; the first capacitor C1 is used for changing the voltage at the first node N1 when the light emission control signal of the first light emission control signal terminal em (N) changes suddenly, so as to maintain a constant voltage difference between two ends of the first capacitor C1.

In one example, the data signal writing module 110 may include a data writing transistor M3 having a gate connected to the data writing control terminal gate (n), a source connected to the data signal terminal date (n), and a drain connected to the source of the driving transistor DTFT. The data writing transistor M3 is used for writing the data signal of the data signal terminal date (n) into the source of the driving transistor DTFT under the control of the writing control signal of the writing control terminal gate (n).

In one example, the driving module 120 may further include a second capacitor C2 connected between the gate of the driving transistor DTFT and the first power voltage terminal ELVDD. The second capacitor C2 is used to maintain the gate voltage of the driving transistor DTFT stable after the compensation of the threshold voltage of the driving transistor DTFT is completed.

In one example, the first power voltage writing module 130 may include a first power voltage writing transistor M4 having a gate connected to the first light emitting control signal terminal em (n), a source connected to the first power voltage terminal ELVDD, and a drain connected to the source of the driving transistor DTFT. The first power voltage writing transistor M4 is used to write the first power voltage of the first power voltage terminal ELVDD to the gate of the driving transistor DTFT under the control of the first light emission control signal terminal em (n).

In one example, the reset module 160 may include a reset transistor M5 having a Gate connected to a reset control terminal Gate (n-1), a source connected to the first terminal of the light emitting module 150, and a drain connected to a reset potential terminal Vint. The reset transistor M5 is used to reset the first terminal of the light emitting module 150 and the Gate of the driving transistor under the control of a reset control signal of the reset control terminal Gate (n-1).

In one example, the light emitting module 150 may include an organic light emitting diode OLED having an anode as a first end of the light emitting module and a cathode as a second end of the light emitting module.

In one example, the light emitting control module 170 may include a light emitting control transistor M6 having a gate connected to the second light emitting control signal terminal EM (n +1), a source connected to the drain of the driving transistor DTFT, and a drain connected to the first terminal of the light emitting module 150. The light emission control transistor M6 is used to transfer the driving current flowing through the driving transistor DTFT to the light emitting module 150 to drive the light emitting module 150 to emit light under the control of the second light emission control signal terminal EM (n + 1).

In addition, in order to ensure that the light emitting device (OLED) does not emit light when the reset potential of the reset potential terminal Vint is transmitted to the first terminal (anode of the OLED) of the light emitting module, it is necessary to satisfy that the anode voltage of the OLED is lower than the cathode voltage thereof, that is, the voltage of the reset signal of the reset potential terminal Vint is lower than the second power voltage of the second power voltage terminal ELVSS.

Of course, in order to ensure subsequent normal light emission of the light emitting device, the first power supply voltage of the first power supply voltage terminal ELVDD should be higher than the second power supply voltage of the second power supply voltage terminal ELVSS.

The embodiment of the present disclosure is described by taking an example in which the threshold compensation transistor M1 is an N-type transistor (oxide N-type transistor), and the driving transistor DTFT, the reference signal writing transistor M2, the data writing transistor M3, the first power voltage writing transistor M4, the reset transistor M5, and the emission control transistor M6 are all P-type transistors. Based on the description and teaching of this implementation manner of the present disclosure, a person of ordinary skill in the art can easily conceive of an implementation manner of the embodiments of the present disclosure using N-type transistors or a combination of N-type and P-type transistors without making creative efforts, and therefore, these implementation manners are also within the protection scope of the present disclosure.

It should be understood that fig. 2 shows only one example circuit structure of the pixel circuit according to the embodiment of the present disclosure, and actually, each block in the pixel circuit may have various circuit structures, and the present disclosure does not limit this.

Embodiments of the present disclosure also provide a method for driving the pixel circuit described above. Specifically, a flowchart of a method for driving the pixel circuit in the above-described embodiment is shown in fig. 3, and an exemplary driving timing chart of the pixel circuit as shown in fig. 1 or fig. 2 is shown in fig. 4, and fig. 5a to 5e show the on states of the respective transistors in the pixel circuit corresponding to the respective stages of T1 to T5 in fig. 3, respectively.

As shown in fig. 3, the driving method includes a data writing and threshold value compensation period T3 and a light emitting period T5 during one frame display period.

In the data write and threshold compensation stage T3, the reference control signal of the reference control terminal Gate (n-2) is set to the second level, the reset control signal of the reset control terminal Gate (n-1) is set to the second level, the data write control signal of the data write control terminal Gate (n) is set to the first level, the first emission control signal of the first emission control signal EM (n) is set to the second level, the second emission control signal of the second emission control signal terminal EM (n +1) is set to the second level, and the data signal of the data signal terminal data (n) is set to the valid data signal.

In the light-emitting period T5, the reference control signal of the reference control terminal Gate (n-2) is set to the second level, the reset control signal of the reset control terminal Gate (n-1) is set to the second level, the data write control signal of the data write control terminal Gate (n) is set to the second level, the first light-emitting control signal of the first light-emitting control signal EM (n) is set to the first level, the second light-emitting control signal of the second light-emitting control signal terminal EM (n +1) is set to the first level, and the data signal of the data signal terminal data (n) is set to the invalid data signal.

In one example, the driving method may further include a first initialization phase T1 and a second initialization phase T2.

Specifically, in the first initialization stage T1, the reference control signal of the reference control terminal Gate (n-2) is set to the first level, the reset control signal of the reset control terminal Gate (n-1) is set to the second level, the data write control signal of the data write control terminal Gate (n) is set to the second level, the first emission control signal of the first emission control signal EM (n) is set to the first level, the second emission control signal of the second emission control signal terminal EM (n +1) is set to the first level, and the data signal of the data signal terminal data (n) is set to the invalid data signal.

In the second initialization stage T2, the reference control signal of the reference control terminal Gate (n-2) is set to the second level, the reset control signal of the reset control terminal Gate (n-1) is set to the first level, the data write control signal of the data write control terminal Gate (n) is set to the second level, the first light emission control signal of the first light emission control signal EM (n) is set to the second level, the second light emission control signal of the second light emission control signal terminal EM (n +1) is set to the first level, and the data signal of the data signal terminal data (n) is set to the invalid data signal.

In one example, the driving method may further include a pre-lighting period T4 after the data writing and threshold value compensating period T3 and before the lighting period T5. In the pre-emission stage, the reference control signal of the reference control terminal Gate (n-2) is set to the second level, the reset control signal of the reset control terminal Gate (n-1) is set to the second level, the data write control signal of the data write control terminal Gate (n) is set to the second level, the first emission control signal of the first emission control signal EM (n) is set to the first level, the second emission control signal of the second emission control signal terminal EM (n +1) is set to the second level, and the data signal of the data signal terminal data (n) is set to the invalid data signal.

In general, the threshold voltage of the threshold compensation transistor shifts after the pixel circuit operates for a certain period of time. For example, if the threshold compensation transistor is an N-type transistor, since the threshold voltage of the N-type transistor is high, the threshold voltage of the N-type transistor will shift toward the negative direction after it has been operated for a certain period of time. In this case, in order to avoid the threshold compensation transistor being turned on when it should be turned off, it is necessary to adjust the voltage signal applied to the gate of the threshold compensation transistor, that is, the reference signal at the reference signal terminal can be adjusted based on the shift of the threshold voltage of the threshold compensation transistor.

In the embodiment of the present disclosure, the first level is the low level VGL, and the second level is the high level VGH. Also, as described previously, in the embodiment of the present disclosure, the threshold compensation transistor is an N-type transistor (specifically, an oxide N-type transistor), and the other transistors are P-type transistors. Because, the first level (low level) is an active level that turns on the threshold compensation transistor M1, and the second level (high level) is an active level that turns on other blocks or other transistors than the threshold compensation transistor.

Of course, the present disclosure does not limit the types of transistors used in the pixel circuit, for example, each transistor may be configured as a P-type or N-type transistor, and it is necessary to turn over the internal connection structure of the pixel circuit and adjust each driving signal.

As shown in fig. 4, in the first initialization period T1, the reference control signal of the reference control terminal Gate (N-2) is at the first level, and the reference signal writing transistor M2 is turned on, so that the reference signal of the reference signal terminal Gate (N-2) is transferred to the first node N1. At this time, the voltage of the first node N1 is the reference signal Vref, and the threshold compensation transistor M1 is turned off. During the first initialization phase T1, the on-state of each transistor is as shown in fig. 5 a.

In the second initialization period T2, the reference control signal of the reference control terminal Gate (n-2) jumps from the first level to the second level, so that the reference signal write transistor M2 is turned off. Meanwhile, the first light emission control signal of the first light emission control signal terminal em (N) jumps from the first level VGL to the second level VGH, pulling up the level of the first node N1, so that the voltage of the first node N1 is Vref + (VGH-VGL). After the potential of the first node N1 becomes high, the threshold compensation transistor M1 is turned on, and the reset control signal of the reset control terminal gate (N) at this time is at the first level, so that the reset transistor M5 is turned on, whereby the reset potential of the reset potential terminal Vint is transferred to the anode of the organic light emitting diode OLED via the reset transistor M5 and further transferred to the gate of the driving transistor DTFT via the threshold compensation transistor M1. Thus, resetting of the anode of the OLED and the gate voltage of the driving transistor DTFT is achieved. At this time, potentials of the anode of the OLED and the gate of the driving transistor DTFT are Vint, and since Vint < ELVSS, the OLED is guaranteed not to emit light. The voltage at the point B is Vint-Vth, so that the voltage difference between the gate and the source of the driving transistor DTFT is Vgs ═ Vth, and the driving transistor DTFT is in a cut-OFF state (OFF Bias is completed) at this time, and the short-term afterimage defect phenomenon of the OLED can be improved. In the second initialization period T2, the on state of each transistor is as shown in fig. 5b, and fig. 5b also shows the current flow of the pixel circuit at this time, i.e. from the reset transistor M5-the emission control transistor M6-the threshold compensation transistor M1, all the way to the gate of the drive transistor.

During the data writing and threshold compensation period T3, the potential of the first node N1 can be maintained at Vref + (VGH-VGL) due to the presence of the first capacitor C1. The reset control signal of the reset control terminal Gate (n-1) jumps from the first level to the second level, and the reset transistor M5 is turned off. The data write control signal of the data write control terminal gate (n) is at the second level, the data signal write transistor M3 is turned on, the data signal of the data signal terminal data (n) is transmitted to the source of the driving transistor DTFT, and the gate voltage of the driving transistor is compensated by the threshold compensation transistor M1. At this time, the source voltage of the driving transistor DTFT is Vdata, and the gate voltage of the compensated driving transistor DTFT is Vdata + Vth. In the data writing and threshold value compensation period T3, the on state of each transistor is as shown in fig. 5c, and fig. 5c also shows the current flow in the pixel circuit at this time, namely from the data writing transistor M3 to the source of the driving transistor DTFT, and to the gate of the driving transistor DTFT.

During the pre-lighting period T4, the first lighting control signal of the first lighting control signal terminal em (n) jumps from the second level to the first level, so that the data signal write transistor M4 is turned on and the first power voltage of the first power voltage terminal ELVDD is transferred to the source of the driving transistor DTFT. And, since em (N) is changed from high to low, the level of the first node N1 is coupled back to Vref by Vref + (VGH-VGL). Due to the presence of the second capacitor C2, the voltage of the gate of the driving transistor DTFT is maintained at Vdata + Vth. In the pre-lighting period T4, the on state of each transistor is shown in fig. 5 d.

In the light emitting period T5, the second light emission control signal of the second light emission control signal terminal EM (n +1) becomes the first level, the light emission control transistor M6 is turned on, and the first power voltage of the first power voltage terminal ELVDD flows into the OLED via the driving current generated by the data write transistor M4, the driving transistor DTFT, and the light emission control transistor M6, driving the OLED to emit light. In the light emission period T5, the on state of each transistor is as shown in fig. 5e, and fig. 5e also shows that the circuit flow in the driving circuit at this time is from the first power supply voltage writing transistor M4-the driving transistor DTFT-the light emission controlling transistor M6, up to the light emitting device OLED.

Drive current I_OLEDThe following saturation current formula is satisfied:

I_OLED＝K(Vgs-Vth)²＝K(Vdata+Vth-ELVDD-Vth)²＝K(Vdata-ELVDD)²

wherein the content of the first and second substances,

μ_nfor the channel mobility of the driving transistor, Cox is the channel capacitance per unit area of the driving transistor, W and L are the channel width and channel length, respectively, of the driving transistor, and Vgs is the gate-source voltage (the difference between the gate voltage and the source voltage of the driving transistor) of the driving transistor.

As can be seen from the above equation, the current flowing through the OLED is independent of the threshold voltage of the driving transistor DTFT. As can be seen, the method for driving the pixel circuit according to the embodiment of the present disclosure better achieves compensation of the threshold voltage of the driving transistor DTFT.

As the operation timing of the respective signals shown in fig. 4, the reference signal write control signal of the reference signal write control terminal Gate (n-2), the reset control signal of the reset control terminal Gate (n-1), and the data write control signal of the data write control terminal Gate (n) may be set to be delayed successively for a certain period of time, and for example, the outputs of the shift registers of the front and rear stages in the pixel circuit may be used as the above three control signals, respectively. And the first light emission control signal of the first light emission control signal terminal EM (n) and the second light emission control signal of the second light emission control signal terminal EM (n +1) are also set to be delayed from each other by a time. The operation timings of the respective signals shown in fig. 4 are merely exemplary, and the present disclosure does not limit them.

Fig. 6 is a graph showing the relationship between the current flowing through itself and the gate-source voltage difference Vg thereof, which is simulated when different threshold voltages are set for the threshold compensation transistor M1 in the pixel circuit shown in fig. 2, and a schematic graph of the current flowing through the OLED during this time.

As mentioned above, when the pixel circuit operates for a period of time, the threshold voltage of the threshold compensation transistor M1 may shift. In the embodiments of the present disclosure, an oxide N-type transistor is used as the threshold compensation transistor, and the threshold voltage thereof may be shifted toward the negative direction. Thus, for example, simulation software such as SmartSpice may be used to obtain a simulation diagram of the current flowing through the threshold compensation transistor M1 at different threshold voltages by setting different threshold voltages to the threshold compensation transistor M1 in the pixel circuit shown in fig. 2. As shown in the upper graph of fig. 6, the threshold voltage of the threshold compensation transistor M1 is set to 0V (before offset) and-5V (after offset), respectively, thus resulting in two corresponding current curves. In the lower graph of fig. 6, the curves of the current through the OLED may be nearly coincident at the different threshold voltage settings described above. This further illustrates that, according to the pixel circuit of the embodiment of the present disclosure, compensation for the threshold voltage of the driving transistor can be well achieved to overcome the defect that the light emitting devices of the respective pixel circuits do not have the same light emitting luminance as each other. As can be seen from the upper diagram of fig. 6, the current of the oxide transistor in the off state is relatively small and gentle. Therefore, when the oxide transistor is used as the threshold compensation transistor, it is ensured that a well-compensated state after Data is written can be maintained more stably after Data voltage writing and threshold voltage compensation for the driving transistor are completed.

Embodiments of the present disclosure also provide a display panel including the pixel circuit provided in any one of the embodiments of the present disclosure.

Embodiments of the present disclosure also provide a display device, which includes the display panel provided above in the present disclosure. For example, the display device may include any product or component with a display function, such as a mobile phone, a tablet computer, a television, a monitor, a notebook computer, a digital photo frame, and a navigator.

Although the present disclosure has been described in detail hereinabove with respect to general illustrations and specific embodiments, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the embodiments of the disclosure. Accordingly, such modifications and improvements are intended to be within the scope of this disclosure, as claimed.

Claims

1. A pixel circuit comprises a data signal writing module, a driving module, a threshold compensation transistor, a first power voltage writing module and a light emitting module, wherein the driving module comprises a driving transistor,

the first power supply voltage writing module is connected with the first light-emitting control signal end, the first power supply voltage end, the source electrode of the driving transistor and the grid electrode of the driving transistor, and is configured to write a first power supply voltage signal of the first power supply voltage end into the source electrode of the driving transistor under the control of the first light-emitting control signal end;

the data signal writing module is connected with the writing control end, the data signal end and the source electrode of the driving transistor and is configured to transmit the data signal of the data signal end to the source electrode of the driving transistor under the control of the writing control signal of the writing control end;

a threshold compensation transistor having a gate connected to the first node, a source connected to the gate of the driving transistor, and a drain connected to the drain of the driving transistor, and configured to perform voltage compensation on the gate of the driving transistor when the first node is at an active level;

a first end of the light emitting module is connected with the drain electrode of the driving transistor, and a second end of the light emitting module is connected with a second power supply voltage end; and

and the reference signal writing module is connected with the reference control terminal, the reference signal terminal, the first light-emitting control signal terminal and the first node, and is configured to control the potential of the first node according to the reference control signal of the reference control terminal and the first light-emitting control signal of the first light-emitting control signal terminal.

2. A pixel circuit as claimed in claim 1, wherein the threshold compensation transistor is an oxide transistor.

3. The pixel circuit of claim 1, wherein the pixel circuit further comprises:

and the reset module is connected with the reset control terminal, the reset potential terminal and the first terminal of the light-emitting module and is configured to reset the first terminal of the light-emitting module and the grid electrode of the driving transistor under the control of a reset control signal of the reset control terminal.

4. The pixel circuit of claim 3, wherein the pixel circuit further comprises:

and the light emitting control module is connected with the second light emitting control signal end, the drain electrode of the driving transistor and the first end of the light emitting module and is configured to drive the light emitting module to emit light under the control of a second light emitting control signal of the second light emitting control signal end.

5. The pixel circuit according to claim 4, wherein the reference signal writing module comprises:

a reference signal writing transistor, the grid of which is connected with the reference control end, the source of which is connected with the first node, and the drain of which is connected with the reference signal end; and the number of the first and second groups,

and a first capacitor connected between the first light emission control signal terminal and the first node.

6. The pixel circuit according to claim 5, wherein the data signal writing module comprises:

and the grid electrode of the data writing transistor is connected with the data writing control end, the source electrode of the data writing transistor is connected with the data signal end, and the drain electrode of the data writing transistor is connected with the source electrode of the driving transistor.

7. The pixel circuit according to claim 6, wherein the first power supply voltage writing module comprises:

and the grid electrode of the first power supply voltage writing transistor is connected with the first light-emitting control signal end, the source electrode of the first power supply voltage writing transistor is connected with the first power supply voltage end, and the drain electrode of the first power supply voltage writing transistor is connected with the source electrode of the driving transistor.

8. The pixel circuit according to claim 7, wherein the driving module further comprises:

and a second capacitor connected between the first power voltage terminal and the gate of the driving transistor.

9. The pixel circuit according to claim 8, wherein the light emission control module comprises:

and the grid electrode of the light-emitting control transistor is connected with the second light-emitting control signal end, the source electrode of the light-emitting control transistor is connected with the drain electrode of the driving transistor, and the drain electrode of the light-emitting control transistor is connected with the first end of the light-emitting module.

10. A pixel circuit as claimed in claim 9, wherein the light emitting module comprises:

and the anode of the OLED is used as the first end of the light-emitting module, and the cathode of the OLED is used as the second end of the light-emitting module.

11. A pixel circuit as claimed in claim 10, wherein the reset block comprises a reset transistor having a gate connected to a reset control terminal, a source connected to the first terminal of the light emitting block, and a drain connected to a reset potential terminal.

12. A pixel circuit as claimed in claim 11, wherein the second power supply voltage of the second power supply voltage terminal is lower than the reset potential of the reset potential terminal.

13. A method of driving a pixel circuit as claimed in any one of claims 1 to 12, comprising:

in a data writing and threshold value compensation stage, a writing control signal of the writing control end is at a first level, a data signal of the data signal end is written into a source electrode of a driving transistor, a reference control signal of the reference control end jumps from the first level to a second level, the level of a first light-emitting control signal jumps from the first level to the second level, the level of a first node is pulled up, and under the control of the first node, the grid potential of the driving transistor is compensated;

in the light emitting stage, the driving current of the driving transistor flows to the light emitting module to drive the light emitting module to emit light.

14. The method of claim 13, wherein the pixel circuit further comprises:

the reference signal writing module is connected with the reference control end, the reference signal end, the first light-emitting control signal end and the first node;

the method further comprises the following steps: a first initialization phase and a second initialization phase,

in a first initialization stage, a reference control signal of a reference control end is in a first level, and the reference signal of the reference control end is transmitted to a first node;

in a second initialization phase, the reference control signal of the reference control terminal jumps from a first level to a second level, the level of the first lighting control signal jumps from the first level to the second level, and the level of the first node is pulled up.

15. The method of claim 14, wherein the pixel circuit further comprises:

the reset module is connected with the reset control end, the reset potential end and the first end of the light-emitting module;

in the second initialization phase, the reset control signal of the reset control end is at the first level, and the reset potential of the reset potential end is transmitted to the first end of the light-emitting module and the grid electrode of the driving transistor.

16. The method of claim 14, wherein the reference signal of the reference signal terminal is adjusted based on a shift of a threshold voltage of a threshold compensation transistor after the pixel circuit operates for a preset time.

17. The method of claim 16, wherein the pixel circuit further comprises:

the light emitting control module is connected with the second light emitting control signal end, the drain electrode of the driving transistor and the first end of the light emitting module;

after the data writing and threshold compensation phase and before the light emitting phase, the method further comprises:

the pre-light-emitting stage is carried out,

in the pre-lighting phase, a first lighting control signal of the first lighting control signal terminal is at a first level, and a first power voltage of the first power voltage terminal is transmitted to the source of the driving transistor.

18. The method of claim 13, wherein the gate potential of the driving transistor is compensated to a sum of the potential of the data signal and the threshold potential of the driving transistor during the data writing and threshold compensation phases.

19. A method as claimed in any one of claims 13 to 17, wherein the first level is lower than the second level.

20. A display panel comprising a pixel circuit as claimed in any one of claims 1 to 12.

21. A display device comprising the display panel according to claim 20.